The research described in this proposal is designed to establish a methodology for studying the separate effects of reinforcer value and reinforcement rate on the behavior of clients with affective disorders. The methodology is based on a current mathematical theory of reinforcer value that has led to the development of a rate equation that expresses response rate on a variable-interval schedule as a joint function of reinforcement rate and reinforcer value. The proposed research is designed to test this bivariate property of the rate equation which, if confirmed, would provide a precise and objective method of studying reinforcement processes in affective disorders. Four normal human subjects will press levers for money in the two phases of the project. In Phase 1, the values of three reinforcer magnitudes (Phi/reinforcer) will be determined in concurrent schedules with variable-interval components. In Phase 2, subjects will work on single-alternative variable-interval schedules that arrange all possible combinations of the three reinforcer magnitudes, and three reinforcement rates. If equilibrium response rates in Phase 2 vary with reinforcer value and reinforcement rate in the manner required by the rate equation, then the theory will be confirmed and the methodology established. The methodology can be used to study the differential ability of reinforcement rate and reinforcer value to maintain the behavior of clients with effective disorders. Empirical information on this issue is important for the proper evaluation of reduced reinforcer value and reduced reinforcement rate theories of depression. The method can also be applied to treatment research, since the relative effects of experimentally arranged changes in reinforcement rate and reinforcer value could be assessed. Relevance to treatment research extends to the evaluation of somatic therapies, since the proposed methods could be used to determine whether medication, like imipramine or lithium, produces changes in reinforcer value and if so, to what extent.